Deployable bow spring centralizer

Abstract

A centralizer sub, and system for enhanced access to subterranean zones from the surf ace as used in oil and gas wellbore installations to center a pipe or casing within a wellbore or previous casing string during run-in, installation, or cementing procedures. In under-reamed applications, casing strings and centralizers pass through a smaller casing string before opening up to a larger hole where repeated compressions and decompressions of bow strings of centralizers can compromise integrity and reliability. A centralizer sub, and system reduces and controls insertion and running forces to preserve centralizer integrity and down-bore surfaces and equipment.

The invention claimed is: 
     
       1. In a casing sub having a deployable bow spring centralizer, a selectively releasable locking mechanism comprising:
 a receptacle; 
 a tab capable of engaging said receptacle; 
 a member to bias said locking mechanism; 
 a first ratchet band capable of circumferential movement about said casing sub, said first ratchet band forming one or more release notches; 
 a second ratchet band capable of circumferential movement about said casing sub, said second ratchet band capable of engagement with said first ratchet band, said second ratchet band forming a notch capable of receiving a spring end; 
 a compression spring having a first end and a second end and fitted around the circumference of said casing sub, said first end forming a spring end; 
 an end band mounted to said casing sub adapted to prevent rotational movement of said end band relative to the casing sub, said end band forming a notch to receive said second end of said compression spring; and 
 a cover fitted around said first ratchet band, said second ratchet band, and said compression spring. 
 
     
     
       2. The releasable locking mechanism of  claim 1  wherein said deployable bow spring centralizer includes said receptacle. 
     
     
       3. The locking mechanism of  claim 1  wherein said second end of said compression spring is adapted to engage the exterior of said casing sub. 
     
     
       4. The locking mechanism of  claim 1  wherein said receptacle is formed as an integral part of said bow spring centralizer. 
     
     
       5. The locking mechanism of  claim 1  wherein said receptacle defines holes, and wherein ball bearings in said holes engage recesses in said casing sub, and wherein upon engagement of said receptacle with said tab, a nose of said tab maintains said ball bearings in said recesses to prevent movement of said bow spring centralizer. 
     
     
       6. The locking mechanism of  claim 1  wherein said receptacle includes pivoting appendages capable of engaging recesses in said casing sub, said pivoting appendages being held apart by engagement with said lock pawl tab. 
     
     
       7. In a casing sub having a deployable bow spring centralizer, a selectively releasable locking mechanism comprising:
 a receptacle connectable to said bow spring centralizer, said receptacle being capable of engaging a corresponding tab and capable of engaging recesses defined in said casing sub; wherein engagement of said receptacle with said tab maintains said bow spring centralizer in a compressed state; 
 a tab affixed to said casing sub and moveable between an engaged position and a disengaged position relative to said receptacle, wherein said tab, in said engaged position, engages said receptacle, and wherein said tab, in said disengaged position, does not restrict movement of said receptacle and said bow spring centralizer; 
 a tab biasing spring, said tab biasing spring having a compressed state and a relaxed state, wherein said tab biasing spring is in its compressed state when said tab is engaged with said receptacle, and wherein said tab biasing spring urges said tab to transition to said disengaged position; 
 a first ratchet band capable of circumferential movement about said casing sub, said first ratchet band having a first edge and a second edge, said first edge forming a release notch to allow said tab to move into said disengaged position, wherein rotational misalignment of said release notch and tab maintains the tab in its engaged position, and wherein alignment of said release notch and tab results in said tab transitioning to its disengaged position, said first edge having formed thereon ratcheting teeth to engage a ratchet spring lock affixed to said casing sub to prevent bi-directional movement of said first ratchet band, and said second edge forming thereon ratcheting teeth; 
 a second ratchet band capable of circumferential movement about said casing sub, said second ratchet band having a first edge and a second edge, said first edge forming ratcheting teeth capable of engagement with said second edge of said first ratchet band so as to allow unidirectional rotation as between said first ratchet band and said second ratchet band, said second edge also forming a notch capable of receiving a spring-end bushing; 
 a spring-end bushing; 
 a compression spring fitted around the circumference of said casing sub, said spring having a first end and a second end, said first end being adapted to engage said spring-end bushing, said second end being adapted to engage a notch, said compression spring ring expanding in response to an increase in the diameter of said casing sub, wherein said compression spring tensions and causes rotation of said second ratchet band and said first ratchet band in a first direction, and wherein said compression spring relaxes in response to a decrease in the diameter of said casing sub and causes rotation of said second ratchet band in a second direction; 
 an end band mounted to said casing sub to prevent rotational movement of said end band relative to the casing sub, said end band formed to receive said second end of said compression spring; and 
 a cover fitted around said first ratchet band, said second ratchet band, and said compression spring. 
 
     
     
       8. The locking mechanism of  claim 7  wherein said receptacle defines holes and wherein ball bearings are inserted into said holes to engage said recesses in said casing sub, and wherein upon engagement of said receptacle with said tab, a nose of said tab maintains said ball bearings in said recesses in said casing sub to prevent movement of said centralizer sub. 
     
     
       9. The locking mechanism of  claim 7  wherein said receptacle includes pivoting appendages capable of engaging said recesses in said casing sub, said pivoting appendages being held apart by engagement with said tab to prevent movement of said centralizer sub. 
     
     
       10. A casing sub having a deployable bow spring centralizer mounted on a casing sub, comprising in axially stackable relation:
 a selectively releasable locking mechanism; first and second ratchet bands; 
 an expandable band comprising at least one compression spring fitted around said casing sub; 
 an end band; and 
 a cover band. 
 
     
     
       11. The casing sub of  claim 10  wherein the expandable band comprises at least one wrap band spring fitted around said casing sub.